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In Ruby on Rails, a polymorphic association is an Active Record association that can connect a model to multiple other models. For example, we can use a single association to connect the Review model with the Event and Restaurant models, allowing us to connect a review with either an event or a restaurant.
Polymorphic association is a term used in discussions of Object-Relational Mapping with respect to the problem of representing in the relational database domain, a relationship from one class to multiple classes.
They can have different numbers of columns, different types of columns. And therefore, because there's just one function which can have many shapes therefore it's called a polymorphic table function. In this presentation I will use example of a specific table, polymorphic table function which is used in a Big SQL.
Polymorphic association, supported by Hibernate, is the solution of such mapping requirement as an instance of entity needs to be associated with one of multiple possible entities. This can be implemented with Any relationship.
Given you have to implement a news feed like the one seen in social networks, ex facebook. Currently I'm using a News class which has a polymorphic assocation which can be of any kind like Image, Comment, Friendship, GroupMembership, etc. Whenever an Object is created, as News is created too. It's working fine with AR(ActiveRecords) but I get into trouble when I'd switch to DM(DataMapper) or Sequel as both don't natevily support polymorphic associations and discourage it's usage.
One workaround would be to use a big SQL clause with lot's of UNIONs to merge all the different tables which should be considered as news. But this has some drawbacks, escpecially performance would be terrible.
So I wonder how to solve without polymorphic associations while still getting good performance and no other drawbacks, like having the possibility of adding meta data to a news?
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